Field
Certain aspects of the present disclosure relate to wireless communication and, more particularly, to management of wireless connections.
Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
In a MIMO system, a wireless terminal may be configured with one of several transmission modes to enable certain features. When a wireless terminal is configured with Mode 7, it may receive downlink control information (DCI) using two possible DCI formats, namely, format 1A and format 1. It is currently proposed that each DCI format correspond to a certain transmission scheme. Specifically, DCI format 1A is used when using a transmit diversity transmission scheme, and format 1 is used in a beamforming transmission scheme. However, each transmission scheme has its own advantages and disadvantages. A “Mode 7” configuration intended to enable a beamforming transmission scheme will improve the directionality and performance of a transmission at the cost of possible channel feedback inaccuracy and latency, whereas a transmission scheme of transmit diversity may be more robust and still effectively utilize faded or weak signals.